The present invention pertains to non-contact dispensing systems for dispensing one or more beads of liquid material onto a substrate, and more particularly to an electrostatic dispensing system for electrostatically dispensing such liquid material.
During electrostatic dispensing operations, a liquid material is electrically biased relative to a target substrate to cause electrostatic attraction between the dispensed liquid material and the substrate for controlled deposition of the liquid material onto the substrate. Prior electrostatic applicators have used charging components directly in the dispensing outlet to create an electrostatic voltage potential between the liquid material being dispensed from the outlet and a grounded substrate. Other applicators, such as disclosed in U.S. patent application Ser. No. 09/429,821 of Borsuk et al., commonly owned by the assignee of the present invention, generate an electrostatic field from beneath a substrate, such as a moving nonwoven web of material. The outlet dispensing the liquid material is grounded to create a voltage potential and thereby cause the dispensed liquid material to be attracted to the substrate and applied in continuous straight lines on the substrate.
Notwithstanding the improvements over the prior art provided by Borsuk et al., further improvements in conventional electrostatic applicators are still desirable. For example, conventional electrostatic applicators of the prior art, including the electrostatic dispensing apparatus disclosed by Borsuk et al., are designed to apply a uniform pattern of dispensed liquid materials to a substrate such that the dispensed liquid materials are applied in straight-line beads. In some applications, it is desired to produce oscillating or other patterns of the dispensed liquid material including patterns in which adjacent beads of dispensed liquid material may overlap. This can be especially desirable in adhesive bead or fiber dispensing applications such as in various packaging operations or product manufacturing operations.
There is a continuing need for an electrostatic dispensing apparatus capable of controlling the placement of a dispensed liquid material onto a moving substrate to provide various patterns of the dispensed liquid material.
The present invention provides an electrostatic dispensing apparatus with the ability to control the placement of one or more beads of liquid, such as a hot melt adhesive, onto a substrate without requiring control or steering of the substrate itself and without requiring controlled movement of the liquid applicator or dispenser. The present invention may be used to control the position of the dispensed liquid bead(s) to form various patterns of the dispensed bead(s) on the substrate.
In one embodiment of the present invention, the electrostatic dispensing apparatus includes a liquid dispensing outlet and an electrostatic point source which is spaced from the liquid dispensing outlet. The term xe2x80x9cpoint source,xe2x80x9d as used herein, is intended to identify structure capable of generating a localized electrostatic field. The electrostatic point source can be moved relative to the liquid dispensing outlet and can be charged to create a voltage potential between the electrostatic point source and the liquid dispensing outlet. As liquid is dispensed from a liquid dispensing outlet which is grounded, for example, it is attracted to the electrostatic point source. The liquid may be electrostatically influenced and thereby deflected during its travel to a substrate in other ways as well, such as by the introduction of secondary electrostatic fields or metallic elements to influence the primary electrostatic field.
The substrate is positioned between the outlet and the point source so that the liquid material dispensed from the outlet will be deposited on the substrate in a precise manner and/or in a specifically desired pattern. Preferably, the substrate moves past a stationary dispensing apparatus. The movement and location of the electrostatic point source may be controlled by any suitable method. For example, position control may be provided by a servo motor coupled to the point source, or by other suitable actuators.
In another embodiment of the present invention, the electrostatic dispensing apparatus includes a plurality of liquid dispensing outlets positioned to dispense a number of liquid beads or fibers onto a substrate which may be moving adjacent to the dispensing apparatus. The device further includes a plurality of electrostatic point sources respectively corresponding to the plurality of liquid dispensing outlets. The electrostatic point sources are aligned to correspond with the liquid dispensing outlets and can be moved to control the position of each of the dispensed liquid beads on the substrate. The electrostatic point sources may be provided on an elongated charging member having multiple extensions to create the individual electrostatic point sources. In a preferred embodiment, the electrostatic point sources are provided on an elongated member having a serrated or scalloped edge to form the individual point sources. The elongated member may be moved relative to the fixed liquid dispensing outlets to control the placement of the dispensed liquid material on the moving substrate.
In yet another embodiment of the present invention, the electrostatic point sources are provided on a rotatable charging rod having raised circumferential ridges disposed on an outer surface of the rod and arranged such that the ridges are positioned on the outer surface at an angle to the longitudinal axis of the rod. In this configuration, the charging rod may be rotated to create the effect of a point source at the position closest to the liquid dispensing outlets. In other words, with respect to the fixed liquid dispensing outlets, the ridges on the rotating rod act as oscillating electrostatic point sources.
In yet another aspect of the present invention, the electrostatic dispensing apparatus includes two or more rows of multiple liquid dispensing outlets positioned adjacent to one another. The electrostatic dispensing apparatus further includes two or more adjacent rows of multiple electrostatic point sources corresponding to each of the rows of liquid dispensing outlets. The rows of electrostatic point sources may be moved either in unison, in groups, or independently to control the placement of the dispensed liquid material on the substrate or to create patterns of the dispensed liquid material on the moving substrate. As illustrative examples, the rows of electrostatic point sources may be provided as either elongated members having serrated or scalloped edges to create the individual electrostatic point sources, or the point sources may be provided as ridges or projections on a charging rod, and the rod may be rotated as described above.
In another aspect of the present invention, a method for dispensing liquid material onto a moving substrate using an electrostatic dispensing apparatus having liquid dispensing outlets and moveable electrostatic point sources includes moving a substrate through a space between the liquid dispensing outlets and the electrostatic point sources. The apparatus dispenses liquid material from the outlets, and the electrostatic point sources generate electrostatic fields which attract the liquid material. The electrostatic point sources move relative to the liquid dispensing outlets to control placement of the liquid material on the moving substrate. During this process, the liquid material is deflected from its normal path out of the outlet by the applied electrostatic force of the point source.
These and other advantages, objectives and features of the invention will become more readily apparent to those of ordinary skill upon review of the following detailed description of an illustrative embodiment of the invention.